In 1959, Richard Feynman addressed a meeting of the American Physical Society with a talk titled “There's Plenty of Room at the Bottom.” Professor Feynman, drawing on his own fascination with biology (“Biological systems can be exceedingly small . . . but they are active; they manufacture substances, they walk around; . . . and they do all kind of marvelous things-all on a very small scale.”), predicted that amazing feats of man-made miniaturization would be realized in the not too distant future.
Twenty-six years later, K. Eric Drexler wrote a book entitled “Engines of Creation” in which he described nanotechnology as “the knowledge and means for designing, fabricating and employing molecular scale devices by the manipulation and placement of individual atoms and molecules with precision on the atomic scale.”
In 1990, Donald Eigler, working in the IBM Almaden Research Center, used the then recently developed scanning probe microscope (SPM) to manipulate 35 individual xenon atoms into the letters IBM on the surface of a crystal of nickel. Since that time a tremendous amount of effort has been, and continues to be, spent on devising practical applications for this new-found ability to work directly with the atom.
In organic chemistry, the quest has not been so much to work with individual atoms as to work with small groups of atoms—molecules—and use them to build, under totally controlled conditions, multimolecular architectures capable of performing, on a submicroscopic scale, functions normally reserved for large-scale constructs. For example, rotaxanes and polyrotaxanes, molecules that are interlocked but not chemically bound to one another, exhibit some mechanical characteristics—they act like micro-machines are being widely studied. Likewise, dendrimers, mono-dispersed macromolecules with a regular and highly branched three-dimensional architecture, also are receiving substantial attention, especially in the area of catalysis. Carbon nanotubes, isolated from the carbon soot on graphite electrodes, have elicited a tremendous amount of interest for a wide range of applications such as strength enhancing fillers for conventional polymers, fuel cell construction, electrical field emitters and quantum wires.
The use of biological processes is also being studied as an approach to the assembly of non-biological nano-devices. For example, in 1995, U.S. Pat. No. 5,468,851, entitled “Construction of Geometrical Objects from Poly-nucleotides,” was issued to Seeman and Zhang. The inventors claimed the ability to produce “ . . . almost any structure one can imagine . . . ” starting with a double stranded polynucleotide segment having a loop at one end that contains a restriction site. The loop is cleaved at the restriction site, and another double stranded polynucleotide segment itself having a loop containing an endonuclease recognizable sequence different from that of the first segment, is ligated to the first segment at the cleavage site. The loop of the second segment is then cleaved and a third polynucleotide segment is ligated into the system. The process is continued until the desired structure is achieved.
The formation of monomolecular thick, selectively permeable membranes was described in 1997 by Hendel, et al., JACS, 1997, 119:6909-18. Hendel and his coworkers reported the synthesis of calix[6]arenes and their deposition as Langmuir-Blodgett films on a porous poly[1(trimethylsilyl)-1-propyne] substrate. They found that, when the calixarenes were positioned on the substrate such that individual calixarene molecules exactly spanned a pore in the substrate, a selectively permeable membrane was formed; i.e., nitrogen was found to pass through the membrane about 10,000 times more slowly than helium.
Another approach to the synthesis of molecular scale constructs was patented in 1999 by Michl, et al. (U.S. Pat. No. 5,876,830). Michl analogized his approach to the children's construction toy “TINKERTOY™” (Playskool, Inc., Pawtucket, R.I.). That is, Michl builds macromolecular structures by linking together complex molecular modules using connectors, spacers, binders, etc. The procedure requires adhering modules to a surface and then reacting connector groups on adjacent modules with molecular “rods” to form monomolecular grids or nets.
In 2001, an international patent application, WO 01/27028 A1, to Spencer and Allis and entitled “Design and Fabrication of Molecular Nanosystems,” published. There, Spencer and Allis describe structural sub-units they term “synthons” which they claim can be used for the design and manufacture of molecular nanostructures, machines and devices. Their synthons are rigid polyhedral structures, namely closocarboranes, which were selected based on their synthetic availability and the fact that they exhibit the requisite substitutional control and structural diversity the inventors considered necessary creation of nano-scale constructs.
For a further review of the above and other areas of research in nanotechnology, see Chemical Reviews, 1999(7).
The present invention provides novel, extremely versatile molecular modules, methods for their synthesis and fabrication into nanoscale devices, in particular selectively permeable membranes.